cxgbe(4): Tidy up the display for payload memory statistics (pm_stats).

# sysctl -n dev.t4nex.0.misc.pm_stats
# sysctl -n dev.t5nex.0.misc.pm_stats

MFC after:	1 week
Propagate ancient fix from Junos.
Use of -h is not supposed to depend on AUTHENTICATION being defined.

Reviewed by: markm